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As part of a series of questions that I've been doing about microscopic humanoids ...

In my world , there are a race of microscopic humanoid organisms ( 0.2 mm - 0.22 mm ) . They live in a variety of biomes , such as leaf litter , stone , and on plants and trees. My questions is -

What weapons would be useful when scaled down to such sizes , especially against small arthropods such as ants and Pseudoscorpions?

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This may be a very difficult question to answer without understanding the magical hocus-pocus that makes the humanoids microscopic. Weapons are typically tailored to hurt an enemy, so we'd need to know what can hurt your miniaturized humanoids, and then act from there. – Cort Ammon Mar 8 at 22:56
This gives a whole new meaning to germ warfare! – Peter Wone Mar 9 at 1:42
@TheoclesofSaturn How did you resolve the issue that humanoid is a really inefficient structure for something that small? – Cort Ammon Mar 9 at 3:08
@TheoclesofSaturn Not everything scales well. Surface tensions, viscocities, things like that don't scale with you. All sorts of things get difficult when you get small. You start to run into limits based on numbers of molecules in your structures when you scale those structures down. The scaled down equivalent of the Stapedius muscle is 1um long. That's on the order of a single algea cell! The eye suffers worse noise floors due to smaller numbers of photons, things like that. – Cort Ammon Mar 9 at 4:25
All of the strengths we have in our body are built to deal with the square-cubed law. Shrink us down, and there's major inefficiencies. – Cort Ammon Mar 9 at 4:26
up vote 24 down vote accepted

Poisons and venoms will likely be important factors in disabling enemies, especially when they are small.

The wide usage of venom by arachnids (spiders, scorpions) and insects (ants, bees, wasps) show that venom is a highly effective means of deterring potential enemies from attacking you at these scales.

Additionally, the fact that venomous insects already exist and are highly common means that the microscopic humanoids do not need to be able to natively produce these venoms, they can simply hunt down the nearest venomous insect and harvest its venom, just like humans do with poison dart frogs.

To obtain these poisonous weapons in the first place, the micro-humans can engage in tactics that normal humans use to hunt prey much larger than themselves.

For example, they could make lassoes from abandoned spider silk that they find in the area. We know lassoes work in insect scales, as bolas spiders are known for using a similar tactic. Alternatively, they could move the spider silk into specific areas, and use it as a trap to defeat the larger venomous insect and then harvest its venom. While using spider silk is likely to be difficult and dangerous, it would guarantee a high success rate and also only has to be done right once in order to allow the humans to use the insect venoms as a weapon.

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I was going to write about exactly the same thing (venom utilization) but you beat me to it. +rep for the practical and objective approach. – Youstay Igo Mar 8 at 17:31
However ... you missed one thing from your answer => how would these little pesky humans hunt down a venomous ant using just microscopic useless weapons and stuff :p – Youstay Igo Mar 8 at 17:32
@YoustayIgo Thanks for the comment. Added a method the micro-humans can use to obtain the venom. – March Ho Mar 8 at 22:58
venom might be fine for a spider scale creature biting a human scale creature, but at 0.2mm a paramecium pushes algae into its mouth groove and attacks it with enzyms – Ewan Mar 9 at 9:02
@ewan This paper measures healthy ants' exoskeletal thickness at around 20um, 10% of the length of a spear. A poisoned spear injecting venom via a joint will probably need to penetrate less material. – March Ho Mar 9 at 9:05

Projectiles will be basically useless. No mass behind them and air would stop them very quickly.

You can take inspiration from existing animals operating at those scales but really the standard solutions of sharp poky things (spears) and sharp slashy things (swords) would work.

I'd expect blunt smashy things (hammers) to be far less effective than at larger sizes for a similar reason to the problem with projectiles. The strength of materials relative to the mass of the hammer is so much higher than at higher scales.

Aiming for weak points in enemies would be far more important as shells/carapaces would be very effective defenses at this scale.

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"[spears and swords] would work" -- against other humanoids. Specifically against ants, you've repeated the premise of the questioner's earlier question:… to which several answers basically say "the humanoids are screwed", because they're so much smaller than the ants. – Steve Jessop Mar 8 at 16:04
@SteveJessop Ahh I wasn't aware of that question. You would need to swarm the ants, climb up the legs and use the spears to aim for vulnerable areas. – Tim B Mar 8 at 16:29
I find it hard to believe that the 0.2mm creature can exert enough force to physicaly pierce the skin of a single celled organism of the same scale. Let alone the exoskeleton of a (5mm?) Ant. Also say you have a glass fibre 0.2mm spear which you plunge full length into the ant. Will it even notice? – Ewan Mar 9 at 0:24
@Ewan Contrary to what you would think, the square-cube law makes the muscles stronger per unit organism mass, so it is likely that it is possible to exert force sufficient to pierce non-armoured regions. – March Ho Mar 9 at 4:23
I think, we need more biology of the creatures. I mean they are too small for muscles as we have them and materials at that scale are so much stronger because of their homogenity – Ewan Mar 9 at 8:58

Chemical weapons or ensnaring attacks would be most useful

Chemical attacks don't care about the size of the target, just its chemical composition. The assassin beetle is a particularly nasty example of chemical weapons on this scale.

In addition to chemical weapons that burn or otherwise disable an opponent, ensnaring your opponent in a sticky secretion would also be effective. Cockroaches use mucus to immobilize attackers.

Also, ants are well known to just rip enemies apart with their giant mandibles. Never discount a giant set of pincers.

Weapons involving the swift application of mass won't work as well at smaller scales

Little things hitting each other is fun to watch when it's small puppets on a stage but on the scale of fractions of a millimeter, it's just not effective. Given the force equation:


as mass goes down, acceleration must go up to compensate. (For the comparison, let's use momentum which avoids figuring out how long it takes for the pollen grain projectile to slow down.)

If a $12~\text{g}$ arrow traveling at $121~\frac{\text{m}}{\text{s}}$ is sufficient to kill a human at $30~\text{m}$, let's scale down to see what happens with our tiny humanoids, while ignoring silly things like general relativity, material strength and fluid viscosity at small scales.

Let's say the tiny humans want to use arrows scaled exactly the same as normal sized humans. The ratio of $50000~\text{g}$ human to $12~\text{g}$ arrow is $4167:1$. Assume that the tiny humanoids weigh $15~\text{mg}$. Their tiny arrow projectiles would weigh: $0.0036~\text{mg} = 3.6~\mu\text{g}$. For size comparison, these tiny humans are shooting tiny grains of pollen at each other.

The momentum of a $0.012~\text{kg} \cdot 121~\frac{\text{m}}{\text{s}} = 1.452~\text{kg} \cdot \frac{\text{m}}{\text{s}}$

To achieve an equivalent momentum for our pollen grain, it will need to be going:

$\frac{1.452~\text{kg} \cdot \frac{\text{m}}{\text{s}}}{1.23\cdot 10^{-11}~\text{kg}} =118048780488~\frac{\text{m}}{\text{s}}$ or about 393 times faster than light.

Note that $c = 299792458~\frac{\text{m}}{\text{s}}$.

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I don't really follow - did you calculate how fast they would need to shoot a microscopic arrow to achieve enough impact to kill a regular sized human? - Shouldn't you rather try to calculate how much speed they would need to kill something in the same scale as them? - You should start with the amount of momentum neccessary to kill an Ant and work from there... – Falco Mar 9 at 11:46
I just saw a video today that explains why hydrogen peroxide is lethal to bacteria and other cells. Might fit in with the chemical section. – Doug Dawson Mar 9 at 19:57

Other Creatures

If they could tame other insects or by use of pheromones control them, they wouldn't need to directly wield weapons themselves and would have access to transport and labour.

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But, if we consider tiny human like us. Why wouldn't we use animals for war. Yes for sure we use them for labour. And in some case, we use horses for cavalry, dogs for scout and Eastern Asia used Elephants. But you don't fight only with those, you need human, for tactics, direction, logistic. – Carlos2W Mar 9 at 15:06
You need humans for war against other humans who will employ clever tactics, but when attacking beasts it's more like hunting and there are many forms of hunting where humans allow creatures to do all the fighting. – Dave Halsall Mar 9 at 15:20

Crushing and cutting weapons, in the sense of jaw-like and scissor-type weapons. Prying, bending, cracking stuff would be the way to go.

The reason for this is that our relative strength increases by a factor of 10 for every decrease in our size for the same number. So if we are only micrometers in size, we have become a million times stronger. At the same time projectile weapons become equally diminished in potency.

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Expanding on March Ho's answer that venom would be the primary weapon for defense and offense.

Which Venom?

Extremely venomous and large spiders' venom. Including

Why only large spiders? Simply because being 0.2 mm means you won't get the inconvenient attention of the spider or be viewed as the next meal. You can just climb up the chelicerae, reach the venom sac and fill up a few gourds.

Other options include the venom of some more frightful monsters (for a 0.2 mm human, these things would be as Eiffel Tower is to us (in perspective of size):

Collecting venom from most of these (all except wasps) is a simple, straightforward method. You are practically invisible to the beast due to your small size. Approach from the back, reach the poison sac, take your fill and dismount. Mission complete.

How To Use?

On spear tips, aimed at the head region. You would want to coat a javelin tip with venom, launch it the head area of your target and run as fast as you can. These stingers would bring the enemy/prey down within around 30 seconds (feels like hours when you are 0.2 mm). You can now rock and roll on the carcass or make a barbecue off of it.

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Can you fill a (microscopic) gourd with the poison? Surface tension would be extremely strong at that scale... – Charles Mar 8 at 20:15
Yes, but microscopic gourds would also be differently constructed than our daily life gourds ;) How about a pot made of the wax you (as a 0.2 mm human) would encounter on the surface of a thick healthy leaf? – Youstay Igo Mar 8 at 21:56
The problem isn't the container, it's the fluid you're trying to fill it with. Press your gourd against it and it would wobble like jelly but not fill the gourd; slam it in and you get sucked into the poison along with the gourd. Or at least that's what I'd expect at that scale. – Charles Mar 8 at 21:58
Different materials have different levels of cohesion and adhesion. It also depends on the venom being electrophilic or electrophobic. p.s. you could always pick up an empty tail of a dead ant (would take 3-4 microscopic humans to do that) and fill it to the brim with venom. That would be equivalent to one drum of venom by our standards. – Youstay Igo Mar 8 at 22:01
@YoustayIgo Actually, it would probably take less than 3-4 micro-humans due to the square-cube law. – March Ho Mar 8 at 23:01

Radioactive weaponry

If your small guys are smart enough and understand more science that we do, you could basically instant-kill living things with the help of gamma rays! If you shoot a radiation so powerful into anything solid, it will excite their atoms so much, that they will to begin to radiate too (sort of a single projectile, which divides into many fragments like in the first 10 seconds of this video).

A high dose of radiation could lead to instant death :)

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+1 for gamma ray idea, -1 for calling that "relativistic weaponry". What's relativistic about that and not relativistic about everything else? – Tomáš Zato Mar 9 at 9:22
Well the particles have basically no mass and travel basically at the speed of light... – Noldor130884 Mar 9 at 14:33
So blinding you with a reflector is now a relativistic weapon? Relativistic weapon typically refers to kinetic energy weapon. – Tomáš Zato Mar 9 at 14:38
Well photons do not have mass, so I guess you are right... Will edit the title of my answer – Noldor130884 Mar 9 at 14:44

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